Does El Niño make fish go hungry?

June 16, 2014

Kirsteen MacKenzie plunges from a STRI research vessel into the Bay of Panama with a snorkel and a net

Kirsteen MacKenzie plunges from a STRI research vessel into the Bay of Panama with a snorkel and a net. She surfaces almost half a minute later and shouts “Success!” In the webbing is a string of salps, gelatinous creatures that will help explain to what extent fish like tuna rely on the bay’s upwelling-driven nutrient bonanza.

“If we know, say, a tuna population is reliant for 20 percent of its body mass on this seasonal upwelling, what happens when a big El Niño event comes in and cuts off the upwelling?” she asks.

Dry season winds push water away from the bay’s shoreline, pulling to the surface cold, nutrient-rich water from the offshore depths. Upwelled nutrients leave distinct chemical imprints on the tissue of marine organisms. These contrast with imprint from areas and seasons without upwelling.

Strong El Niño events may suppress upwelling by delivering an immovable mass of warm surface water to the bay. This can have profound consequences on the bay’s food web. Creatures like salps, which are fairly immobile when compared to big fish, are ideal creatures for tracking the accompanying chemical changes in specific places. MacKenzie compares the signature of the salps to those apex predators like tuna, sharks and whales, and determines where and when they eat.

MacKenzie, this year’s Smithsonian Stable Isotopes Fellow, hopes her research will contribute to effective management and conservation of fisheries, and help predict the impact of upwelling variation under different future climate scenarios.